The present invention relates to improved breakdown voltages in trench devices, and in particular, to trench devices having improved breakdown voltages and method for manufacturing same.
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Some semiconductor power devices use trenching to produce metal-oxide-semiconductor (MOS) devices that increase efficiency. For example, rectifiers may be comprised of an array of diodes. Each diode has a PN junction which may dissipate power due to the turn on voltage of the PN junction. This turn on voltage of about 0.6V may be reduced by a trenched MOS gate fabricated vertically within a trench to form a vertical MOS device within the semiconductor. The MOS device may turn on at a few tenths of a volt, and thereby reduce the voltage drop across the PN junction. This, in turn, reduces the power dissipation associated with that voltage drop. The rectifier turns off when a reverse voltage is placed across its terminals.
When the rectifier is biased with a reverse voltage, no significant current flows. In some applications the rectifier may experience transient reverse voltages over 70V, and the ability for the rectifier to withstand such transient voltages without breaking down is a measure of reliability. The breakdown voltage of a rectifier using trenched gates may be defined by the trenched MOS gate structure.
The trenched MOS gate is insulated from the cathode region of the diode by a dielectric. During the reverse bias voltage condition, a voltage V forms across this dielectric. In this case, the trenched gate dielectric may have a voltage breakdown that is lower than the breakdown of the PN junctions of the diodes themselves. This premature breakdown may limit the operational voltages which may be used with the rectifier or may cause reliability problems.
Thus, there is a need for improved breakdown voltages in trench devices. The present invention solves these and other problems by providing trench devices having improved breakdown voltages and method for manufacturing same.